path: root/libX11/specs/libX11/CH09

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.sp 1
.ce 3
\s+1\fBChapter 9\fP\s-1

\s+1\fBWindow and Session Manager Functions\fP\s-1
.sp 2
.nr H1 9
.nr H2 0
.nr H3 0
.nr H4 0
.nr H5 0
.na
.LP
.XS
Chapter 9: Window and Session Manager Functions 
.XE
Although it is difficult to categorize functions as exclusively
for an application, a window manager, or a session manager,
the functions in this chapter are most often used by window managers
and session managers.
It is not expected that these functions will be used by most 
application programs.
Xlib provides management functions to:
.IP \(bu 5
Change the parent of a window
.IP \(bu 5
Control the lifetime of a window
.IP \(bu 5
Manage installed colormaps
.IP \(bu 5
Set and retrieve the font search path
.IP \(bu 5
Grab the server
.IP \(bu 5
Kill a client
.IP \(bu 5
Control the screen saver
.IP \(bu 5
Control host access
.NH 2
Changing the Parent of a Window
.XS
\*(SN Changing the Parent of a Window 
.XE
.LP
To change a window's parent to another window on the same screen, use
.PN XReparentWindow .
There is no way to move a window between screens.
.IN "XReparentWindow" "" "@DEF@"
.sM
.FD 0
XReparentWindow\^(\^\fIdisplay\fP, \fIw\fP\^, \fIparent\fP\^, \fIx\fP\^, \fIy\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Window \fIw\fP\^;
.br
      Window \fIparent\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIw\fP 1i
Specifies the window.
.IP \fIparent\fP 1i
Specifies the parent window.
.ds Xy \ of the position in the new parent window
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.LP
.eM
If the specified window is mapped,
.PN XReparentWindow
automatically performs an
.PN UnmapWindow
request on it, removes it from its current position in the hierarchy,
and inserts it as the child of the specified parent.
The window is placed in the stacking order on top with respect to
sibling windows.
.LP
After reparenting the specified window,
.PN XReparentWindow
causes the X server to generate a
.PN ReparentNotify
event.
The override_redirect member returned in this event is
set to the window's corresponding attribute.
Window manager clients usually should ignore this window if this member
is set to
.PN True .
Finally, if the specified window was originally mapped,
the X server automatically performs a
.PN MapWindow
request on it.
.LP
The X server performs normal exposure processing on formerly obscured
windows.
The X server might not generate 
.PN Expose 
events for regions from the initial
.PN UnmapWindow
request that are immediately obscured by the final
.PN MapWindow
request.
A
.PN BadMatch
error results if:
.IP \(bu 5
The new parent window is not on the same screen as
the old parent window.
.IP \(bu 5
The new parent window is the specified window or an inferior of the
specified window.
.IP \(bu 5
The new parent is
.PN InputOnly ,
and the window is not.
.IP \(bu 5
The specified window has a
.PN ParentRelative
background, and the new parent window is not the same depth as the
specified window.
.LP
.PN XReparentWindow
can generate
.PN BadMatch
and
.PN BadWindow 
errors.
.NH 2
Controlling the Lifetime of a Window
.XS
\*(SN Controlling the Lifetime of a Window 
.XE
.LP
The save-set of a client is a list of other clients' windows that,
if they are inferiors of one of the client's windows at connection close,
should not be destroyed and should be remapped if they are unmapped.
For further information about close-connection processing,
see section 2.6.
To allow an application's window to survive when a window manager that
has reparented a window fails,
Xlib provides the save-set functions that you can 
use to control the longevity of subwindows
that are normally destroyed when the parent is destroyed.
For example, a window manager that wants to add decoration
to a window by adding a frame might reparent an application's
window. 
When the frame is destroyed,
the application's window should not be destroyed 
but be returned to its previous place in the window hierarchy.
.LP
The X server automatically removes windows from the save-set
when they are destroyed.
.LP
.sp
To add or remove a window from the client's save-set, use
.PN XChangeSaveSet .
.IN "XChangeSaveSet" "" "@DEF@"
.sM
.FD 0
XChangeSaveSet\^(\^\fIdisplay\fP, \fIw\fP\^, \fIchange_mode\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Window \fIw\fP\^;
.br
      int \fIchange_mode\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.ds Wi that you want to add to or delete from the client's save-set
.IP \fIw\fP 1i
Specifies the window \*(Wi.
.IP \fIchange_mode\fP 1i
Specifies the mode.
You can pass
.PN SetModeInsert 
or
.PN SetModeDelete .
.LP
.eM
Depending on the specified mode,
.PN XChangeSaveSet
either inserts or deletes the specified window from the client's save-set. 
The specified window must have been created by some other client,
or a
.PN BadMatch
error results.
.LP
.PN XChangeSaveSet
can generate
.PN BadMatch ,
.PN BadValue ,
and
.PN BadWindow 
errors.
.LP
.sp
To add a window to the client's save-set, use
.PN XAddToSaveSet .
.IN "XAddToSaveSet" "" "@DEF@"
.sM
.FD 0
XAddToSaveSet\^(\^\fIdisplay\fP, \fIw\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Window \fIw\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.ds Wi that you want to add to the client's save-set
.IP \fIw\fP 1i
Specifies the window \*(Wi.
.LP
.eM
The
.PN XAddToSaveSet
function adds the specified window to the client's save-set.
The specified window must have been created by some other client,
or a
.PN BadMatch
error results.
.LP
.PN XAddToSaveSet
can generate
.PN BadMatch
and
.PN BadWindow 
errors.
.LP
.sp
To remove a window from the client's save-set, use
.PN XRemoveFromSaveSet .
.IN "XRemoveFromSaveSet" "" "@DEF@"
.sM
.FD 0
XRemoveFromSaveSet\^(\^\fIdisplay\fP, \fIw\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Window \fIw\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.ds Wi that you want to delete from the client's save-set
.IP \fIw\fP 1i
Specifies the window \*(Wi.
.LP
.eM
The
.PN XRemoveFromSaveSet
function removes the specified window from the client's save-set.
The specified window must have been created by some other client,
or a
.PN BadMatch
error results.
.LP
.PN XRemoveFromSaveSet
can generate
.PN BadMatch 
and
.PN BadWindow 
errors.
.NH 2
Managing Installed Colormaps
.XS
\*(SN Managing Installed Colormaps
.XE
.LP
The X server maintains a list of installed colormaps.
Windows using these colormaps are guaranteed to display with
correct colors; windows using other colormaps may or may not display
with correct colors.
Xlib provides functions that you can use to install a colormap, 
uninstall a colormap, and obtain a list of installed colormaps.
.LP
At any time,
there is a subset of the installed maps that is viewed as an ordered list
and is called the required list.
The length of the required list is at most M,
where M is the minimum number of installed colormaps specified for the screen
in the connection setup.
The required list is maintained as follows.
When a colormap is specified to
.PN XInstallColormap ,
it is added to the head of the list;
the list is truncated at the tail, if necessary, to keep its length to 
at most M.
When a colormap is specified to
.PN XUninstallColormap
and it is in the required list,
it is removed from the list.
A colormap is not added to the required list when it is implicitly installed
by the X server,
and the X server cannot implicitly uninstall a colormap that is in the
required list.
.LP
.sp
To install a colormap, use
.PN XInstallColormap .
.IN "XInstallColormap" "" "@DEF@"
.sM
.FD 0
XInstallColormap\^(\^\fIdisplay\fP, \fIcolormap\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Colormap \fIcolormap\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIcolormap\fP 1i
Specifies the colormap.
.LP
.eM
The
.PN XInstallColormap
function installs the specified colormap for its associated screen.
All windows associated with this colormap immediately display with
true colors.
You associated the windows with this colormap when you created them by calling
.PN XCreateWindow ,
.PN XCreateSimpleWindow ,
.PN XChangeWindowAttributes ,
or
.PN XSetWindowColormap .
.LP
If the specified colormap is not already an installed colormap, 
the X server generates a
.PN ColormapNotify
event on each window that has that colormap.
In addition, for every other colormap that is installed as 
a result of a call to
.PN XInstallColormap ,
the X server generates a
.PN ColormapNotify
event on each window that has that colormap.
.LP
.PN XInstallColormap
can generate a
.PN BadColor 
error.
.LP
.sp
To uninstall a colormap, use
.PN XUninstallColormap .
.IN "XUninstallColormap" "" "@DEF@"
.sM
.FD 0
XUninstallColormap\^(\^\fIdisplay\fP, \fIcolormap\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Colormap \fIcolormap\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIcolormap\fP 1i
Specifies the colormap.
.LP
.eM
The
.PN XUninstallColormap
function removes the specified colormap from the required
list for its screen.
As a result,
the specified colormap might be uninstalled, 
and the X server might implicitly install or uninstall additional colormaps.
Which colormaps get installed or uninstalled is server dependent
except that the required list must remain installed.
.LP
If the specified colormap becomes uninstalled, 
the X server generates a
.PN ColormapNotify
event on each window that has that colormap.
In addition, for every other colormap that is installed or uninstalled as a 
result of a call to 
.PN XUninstallColormap ,
the X server generates a
.PN ColormapNotify
event on each window that has that colormap.
.LP
.PN XUninstallColormap
can generate a
.PN BadColor 
error.
.LP
.sp
To obtain a list of the currently installed colormaps for a given screen, use
.PN XListInstalledColormaps .
.IN "XListInstalledColormaps" "" "@DEF@"
.sM
.FD 0
Colormap *XListInstalledColormaps\^(\^\fIdisplay\fP, \fIw\fP, \fInum_return\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Window \fIw\fP\^;
.br
      int *\fInum_return\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.ds Wi that determines the screen
.IP \fIw\fP 1i
Specifies the window \*(Wi.
.IP \fInum_return\fP 1i
Returns the number of currently installed colormaps.
.LP
.eM
The
.PN XListInstalledColormaps
function returns a list of the currently installed colormaps for the screen 
of the specified window.
The order of the colormaps in the list is not significant
and is no explicit indication of the required list.
When the allocated list is no longer needed,
free it by using
.PN XFree .
.LP
.PN XListInstalledColormaps
can generate a
.PN BadWindow 
error.
.NH 2
Setting and Retrieving the Font Search Path
.XS
\*(SN Setting and Retrieving the Font Search Path 
.XE
.LP
The set of fonts available from a server depends on a font
search path.  Xlib provides functions to set and retrieve the
search path for a server.
.LP
.sp
To set the font search path, use
.PN XSetFontPath .
.IN "XSetFontPath" "" "@DEF@"
.sM
.FD 0
XSetFontPath\^(\^\fIdisplay\fP, \fIdirectories\fP\^, \fIndirs\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      char **\fIdirectories\fP\^;
.br
      int \fIndirs\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIdirectories\fP 1i
Specifies the directory path used to look for a font.
Setting the path to the empty list restores the default path defined
for the X server.
.IP \fIndirs\fP 1i
Specifies the number of directories in the path.
.LP
.eM
The
.PN XSetFontPath
function defines the directory search path for font lookup.
There is only one search path per X server, not one per client.
The encoding and interpretation of the strings are implementation-dependent,
but typically they specify directories or font servers to be searched 
in the order listed.
An X server is permitted to cache font information internally;
for example, it might cache an entire font from a file and not
check on subsequent opens of that font to see if the underlying
font file has changed.
However,
when the font path is changed,
the X server is guaranteed to flush all cached information about fonts 
for which there currently are no explicit resource IDs allocated.
The meaning of an error from this request is implementation-dependent.
.LP
.PN XSetFontPath
can generate a
.PN BadValue 
error.
.LP
.sp
To get the current font search path, use
.PN XGetFontPath .
.IN "XGetFontPath" "" "@DEF@"
.sM
.FD 0
char **XGetFontPath\^(\^\fIdisplay\fP, \fInpaths_return\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      int *\fInpaths_return\fP\^;

.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fInpaths_return\fP 1i
Returns the number of strings in the font path array.
.LP
.eM
The
.PN XGetFontPath
function allocates and returns an array of strings containing the search path.
The contents of these strings are implementation-dependent
and are not intended to be interpreted by client applications.
When it is no longer needed,
the data in the font path should be freed by using
.PN XFreeFontPath .
.LP
.sp
To free data returned by
.PN XGetFontPath ,
use
.PN XFreeFontPath .
.IN "XFreeFontPath" "" "@DEF@"
.sM
.FD 0
XFreeFontPath\^(\^\fIlist\fP\^)
.br
      char **\fIlist\fP\^;

.FN
.IP \fIlist\fP 1i
Specifies the array of strings you want to free.
.LP
.eM
The
.PN XFreeFontPath
function
frees the data allocated by
.PN XGetFontPath .
.NH 2
Grabbing the Server 
.XS
\*(SN Grabbing the Server 
.XE
.LP
Xlib provides functions that you can use to grab and ungrab the server.
These functions can be used to control processing of output on other
connections by the window system server.
While the server is grabbed,
no processing of requests or close downs on any other connection will occur.
A client closing its connection automatically ungrabs the server.
.IN "Menus"
.IN "Window" "managers"
Although grabbing the server is highly discouraged, it is sometimes necessary.
.LP
.sp
To grab the server, use
.PN XGrabServer .
.IN "Server" "grabbing"
.IN "Grabbing" "server"
.IN "XGrabServer" "" "@DEF@"
.sM
.FD 0
XGrabServer\^(\^\fIdisplay\fP\^)
.br
      Display *\fIdisplay\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.LP
.eM
The
.PN XGrabServer
function disables processing of requests and close downs on all other 
connections than the one this request arrived on.
You should not grab the X server any more than is absolutely necessary.
.LP
.sp
To ungrab the server, use
.PN XUngrabServer .
.IN "XUngrabServer" "" "@DEF@"
.sM
.FD 0
XUngrabServer\^(\^\fIdisplay\fP\^)
.br
      Display *\fIdisplay\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.LP
.eM
The
.PN XUngrabServer
function restarts processing of requests and close downs on other connections.
You should avoid grabbing the X server as much as possible.
.NH 2
Killing Clients
.XS
\*(SN Killing Clients 
.XE
.LP
Xlib provides a function to cause the connection to
a client to be closed and its resources to be destroyed.
To destroy a client, use
.PN XKillClient .
.IN "XKillClient" "" "@DEF@"
.sM
.FD 0
XKillClient\^(\^\fIdisplay\fP, \fIresource\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      XID \fIresource\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIresource\fP 1i
Specifies any resource associated with the client that you want to destroy or
.PN AllTemporary .
.LP
.eM
The
.PN XKillClient
function
forces a close down of the client
that created the resource
if a valid resource is specified.
If the client has already terminated in
either 
.PN RetainPermanent 
or 
.PN RetainTemporary 
mode, all of the client's
resources are destroyed.
If 
.PN AllTemporary 
is specified, the resources of all clients that have terminated in
.PN RetainTemporary 
are destroyed (see section 2.5).
This permits implementation of window manager facilities that aid debugging.
A client can set its close-down mode to
.PN RetainTemporary .
If the client then crashes,
its windows would not be destroyed. 
The programmer can then inspect the application's window tree 
and use the window manager to destroy the zombie windows.
.LP
.PN XKillClient
can generate a
.PN BadValue 
error.
.NH 2
Controlling the Screen Saver 
.XS
\*(SN Controlling the Screen Saver 
.XE
.LP
Xlib provides functions that you can use to set or reset the mode 
of the screen saver, to force or activate the screen saver,
or to obtain the current screen saver values.
.LP
.sp
To set the screen saver mode, use
.PN XSetScreenSaver .
.IN "XSetScreenSaver" "" "@DEF@"
.sM
.FD 0
XSetScreenSaver\^(\^\fIdisplay\fP, \fItimeout\fP\^, \fIinterval\fP\^, \fIprefer_blanking\fP\^, \fIallow_exposures\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      int \fItimeout\fP\^, \fIinterval\fP\^;
.br
      int \fIprefer_blanking\fP\^; 
.br
      int \fIallow_exposures\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fItimeout\fP 1i
Specifies the timeout, in seconds, until the screen saver turns on.
.IP \fIinterval\fP 1i
Specifies the interval, in seconds, between screen saver alterations.
.IP \fIprefer_blanking\fP 1i
Specifies how to enable screen blanking.
You can pass
.PN DontPreferBlanking ,
.PN PreferBlanking ,
or
.PN DefaultBlanking .
.IP \fIallow_exposures\fP 1i
Specifies the screen save control values.
You can pass
.PN DontAllowExposures ,
.PN AllowExposures ,
or
.PN DefaultExposures .
.LP
.eM
Timeout and interval are specified in seconds. 
A timeout of 0 disables the screen saver 
(but an activated screen saver is not deactivated),
and a timeout of \-1 restores the default.
Other negative values generate a
.PN BadValue
error.
If the timeout value is nonzero, 
.PN XSetScreenSaver
enables the screen saver.
An interval of 0 disables the random-pattern motion.
If no input from devices (keyboard, mouse, and so on) is generated 
for the specified number of timeout seconds once the screen saver is enabled,
the screen saver is activated.
.LP
For each screen, 
if blanking is preferred and the hardware supports video blanking, 
the screen simply goes blank.  
Otherwise, if either exposures are allowed or the screen can be regenerated 
without sending 
.PN Expose 
events to clients, 
the screen is tiled with the root window background tile randomly 
re-origined each interval seconds.
Otherwise, the screens' state do not change, 
and the screen saver is not activated.
The screen saver is deactivated,
and all screen states are restored at the next
keyboard or pointer input or at the next call to
.PN XForceScreenSaver
with mode
.PN ScreenSaverReset .  
.LP
If the server-dependent screen saver method supports periodic change,
the interval argument serves as a hint about how long the change period
should be, and zero hints that no periodic change should be made.
Examples of ways to change the screen include scrambling the colormap
periodically, moving an icon image around the screen periodically, or tiling
the screen with the root window background tile, randomly re-origined
periodically.
.LP
.PN XSetScreenSaver
can generate a
.PN BadValue 
error.
.LP
.sp
To force the screen saver on or off, use
.PN XForceScreenSaver .
.IN "XForceScreenSaver" "" "@DEF@"
.sM
.FD 0
XForceScreenSaver\^(\^\fIdisplay\fP\^, \fImode\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      int \fImode\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fImode\fP 1i
Specifies the mode that is to be applied.
You can pass
.PN ScreenSaverActive
or
.PN ScreenSaverReset .
.LP
.eM
If the specified mode is 
.PN ScreenSaverActive 
and the screen saver currently is deactivated,
.PN XForceScreenSaver
activates the screen saver even if the screen saver had been disabled
with a timeout of zero.
If the specified mode is 
.PN ScreenSaverReset 
and the screen saver currently is enabled,
.PN XForceScreenSaver
deactivates the screen saver if it was activated,
and the activation timer is reset to its initial state 
(as if device input had been received).
.LP
.PN XForceScreenSaver
can generate a
.PN BadValue 
error.
.LP
.sp
To activate the screen saver, use
.PN XActivateScreenSaver .
.IN "XActivateScreenSaver" "" "@DEF@"
.sM
.FD 0
XActivateScreenSaver\^(\^\fIdisplay\fP\^)
.br
      Display *\fIdisplay\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.LP
.eM
.sp
To reset the screen saver, use
.PN XResetScreenSaver .
.IN "XResetScreenSaver" "" "@DEF@"
.sM
.FD 0
XResetScreenSaver\^(\^\fIdisplay\fP\^)
.br
      Display *\fIdisplay\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.LP
.eM
.sp
To get the current screen saver values, use
.PN XGetScreenSaver .
.IN "XGetScreenSaver" "" "@DEF@"
.sM
.FD 0
XGetScreenSaver\^(\^\fIdisplay\fP, \fItimeout_return\fP\^, \fIinterval_return\fP\^, \fIprefer_blanking_return\fP\^, 
.br
                  \fIallow_exposures_return\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      int *\fItimeout_return\fP\^, *\fIinterval_return\fP\^;
.br
      int *\fIprefer_blanking_return\fP\^;
.br
      int *\fIallow_exposures_return\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fItimeout_return\fP 1i
Returns the timeout, in seconds, until the screen saver turns on.
.IP \fIinterval_return\fP 1i
Returns the interval between screen saver invocations.
.IP \fIprefer_blanking_return\fP 1i
Returns the current screen blanking preference
.Pn ( DontPreferBlanking ,
.PN PreferBlanking ,
or
.PN DefaultBlanking ).
.IP \fIallow_exposures_return\fP 1i
Returns the current screen save control value
.Pn ( DontAllowExposures ,
.PN AllowExposures ,
or
.PN DefaultExposures ).
.LP
.eM
.NH 2
Controlling Host Access
.XS
\*(SN Controlling Host Access 
.XE
.LP
This section discusses how to:
.IP \(bu 5
Add, get, or remove hosts from the access control list
.IP \(bu 5
Change, enable, or disable access
.LP
.IN "Access control list"
.IN "Authentication"
X does not provide any protection on a per-window basis.
If you find out the resource ID of a resource, you can manipulate it.
To provide some minimal level of protection, however,
connections are permitted only from machines you trust.
This is adequate on single-user workstations but obviously
breaks down on timesharing machines.
Although provisions exist in the X protocol for proper connection
authentication, the lack of a standard authentication server
leaves host-level access control as the only common mechanism.
.LP
.IN "Default Protection"
The initial set of hosts allowed to open connections typically consists of:
.IP \(bu 5
The host the window system is running on.
.IP \(bu 5
On POSIX-conformant systems, each host listed in the
.PN /etc/X?.hosts 
file.
The ? indicates the number of the
display.
.IN "Files" "/etc/X?.hosts"
This file should consist of host names separated by newlines.
DECnet nodes must terminate in :: to distinguish them from Internet hosts.
.LP
If a host is not in the access control list when the access control 
mechanism is enabled and if the host attempts to establish a connection,
the server refuses the connection.
To change the access list,
the client must reside on the same host as the server and/or must
have been granted permission in the initial authorization at connection
setup.
.LP
Servers also can implement other access control policies in addition to
or in place of this host access facility.
For further information about other access control implementations,
see ``X Window System Protocol.''
.NH 3
Adding, Getting, or Removing Hosts
.XS
\*(SN Adding, Getting, or Removing Hosts 
.XE
.LP
Xlib provides functions that you can use to add, get, or remove hosts
from the access control list.
All the host access control functions use the 
.PN XHostAddress 
structure, which contains:
.LP
.IN "XHostAddress" "" "@DEF@"
.sM
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	int family;	/* for example FamilyInternet */
	int length;	/* length of address, in bytes */
	char *address;	/* pointer to where to find the address */
} XHostAddress;
.De
.LP
.eM
The family member specifies which protocol address family to use 
(for example, TCP/IP or DECnet) and can be
.PN FamilyInternet ,
.PN FamilyInternet6 ,
.PN FamilyServerInterpreted ,
.PN FamilyDECnet ,
or
.PN FamilyChaos .
The length member specifies the length of the address in bytes.
The address member specifies a pointer to the address.
.LP
For TCP/IP, the address should be in network byte order.
For IP version 4 addresses, the family should be FamilyInternet
and the length should be 4 bytes.  For IP version 6 addresses, the
family should be FamilyInternet6 and the length should be 16 bytes.
.LP
For the DECnet family, 
the server performs no automatic swapping on the address bytes.
A Phase IV address is 2 bytes long.
The first byte contains the least significant 8 bits of the node number.
The second byte contains the most significant 2 bits of the
node number in the least significant 2 bits of the byte
and the area in the most significant 6 bits of the byte.
.LP
For the ServerInterpreted family, the length is ignored and the address 
member is a pointer to a 
.PN XServerInterpretedAddress
structure, which contains:
.LP
.IN "XServerInterpretedAddress" "" "@DEF@"
.sM
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	int typelength;	/* length of type string, in bytes */
	int valuelength;/* length of value string, in bytes */
	char *type;	/* pointer to where to find the type string */
	char *value;	/* pointer to where to find the address */
} XServerInterpretedAddress;
.De
.LP
.eM
The type and value members point to strings representing the type and value of
the server interpreted entry.  These strings may not be NULL-terminated so care
should be used when accessing them.  The typelength and valuelength members
specify the length in byte of the type and value strings.
.LP
.sp
To add a single host, use
.PN XAddHost .
.IN "XAddHost" "" "@DEF@"
.sM
.FD 0
XAddHost\^(\^\fIdisplay\fP, \fIhost\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      XHostAddress *\fIhost\fP\^;	
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.ds Ho added
.IP \fIhost\fP 1i
Specifies the host that is to be \*(Ho.
.LP
.eM
The
.PN XAddHost
function adds the specified host to the access control list for that display.
The server must be on the same host as the client issuing the command, or a
.PN BadAccess
error results.
.LP
.PN XAddHost
can generate
.PN BadAccess
and
.PN BadValue 
errors.
.LP
.sp
To add multiple hosts at one time, use
.PN XAddHosts .
.IN "XAddHosts" "" "@DEF@"
.sM
.FD 0
XAddHosts\^(\^\fIdisplay\fP, \fIhosts\fP, \fInum_hosts\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      XHostAddress *\fIhosts\fP\^;
.br
      int \fInum_hosts\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.ds Ho added
.IP \fIhosts\fP 1i
Specifies each host that is to be \*(Ho.
.IP \fInum_hosts\fP 1i
Specifies the number of hosts.
.LP
.eM
The
.PN XAddHosts
function adds each specified host to the access control list for that display.
The server must be on the same host as the client issuing the command, or a
.PN BadAccess
error results.
.LP
.PN XAddHosts
can generate
.PN BadAccess
and
.PN BadValue 
errors.
.LP
.sp
To obtain a host list, use
.PN XListHosts .
.IN "XListHosts" "" "@DEF@"
.sM
.FD 0
XHostAddress *XListHosts\^(\^\fIdisplay\fP, \fInhosts_return\fP, \fIstate_return\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      int *\fInhosts_return\fP\^;
.br
      Bool *\fIstate_return\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fInhosts_return\fP 1i
Returns the number of hosts currently in the access control list.
.IP \fIstate_return\fP 1i
Returns the state of the access control.
.LP
.eM
The
.PN XListHosts
function returns the current access control list as well as whether the use 
of the list at connection setup was enabled or disabled.
.PN XListHosts
allows a program to find out what machines can make connections.
It also returns a pointer to a list of host structures that
were allocated by the function. 
When no longer needed,
this memory should be freed by calling
.PN XFree .
.LP
.sp
To remove a single host, use
.PN XRemoveHost .
.IN "XRemoveHost" "" "@DEF@"
.sM
.FD 0
XRemoveHost\^(\^\fIdisplay\fP, \fIhost\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      XHostAddress *\fIhost\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.ds Ho removed
.IP \fIhost\fP 1i
Specifies the host that is to be \*(Ho.
.LP
.eM
The
.PN XRemoveHost
function removes the specified host from the access control list 
for that display.
The server must be on the same host as the client process, or a
.PN BadAccess
error results.
If you remove your machine from the access list,
you can no longer connect to that server,
and this operation cannot be reversed unless you reset the server.
.LP
.PN XRemoveHost
can generate
.PN BadAccess
and
.PN BadValue 
errors.
.LP
.sp
To remove multiple hosts at one time, use
.PN XRemoveHosts .
.IN "XRemoveHosts" "" "@DEF@"
.sM
.FD 0
XRemoveHosts\^(\^\fIdisplay\fP, \fIhosts\fP, \fInum_hosts\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      XHostAddress *\fIhosts\fP\^;
.br
      int \fInum_hosts\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.ds Ho removed
.IP \fIhosts\fP 1i
Specifies each host that is to be \*(Ho.
.IP \fInum_hosts\fP 1i
Specifies the number of hosts.
.LP
.eM
The
.PN XRemoveHosts
function removes each specified host from the access control list for that 
display.  
The X server must be on the same host as the client process, or a
.PN BadAccess
error results.
If you remove your machine from the access list, 
you can no longer connect to that server,
and this operation cannot be reversed unless you reset the server.
.LP
.PN XRemoveHosts
can generate
.PN BadAccess
and
.PN BadValue 
errors.
.NH 3
Changing, Enabling, or Disabling Access Control
.XS
\*(SN Changing, Enabling, or Disabling Access Control 
.XE
.LP
Xlib provides functions that you can use to enable, disable, 
or change access control.
.LP
For these functions to execute successfully,
the client application must reside on the same host as the X server
and/or have been given permission in the initial authorization
at connection setup.
.LP
.sp
To change access control, use
.PN XSetAccessControl .
.IN "XSetAccessControl" "" "@DEF@"
.sM
.FD 0
XSetAccessControl\^(\^\fIdisplay\fP, \fImode\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      int \fImode\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fImode\fP 1i
Specifies the mode.
You can pass
.PN EnableAccess
or
.PN DisableAccess .
.LP
.eM
The
.PN XSetAccessControl
function either enables or disables the use of the access control list 
at each connection setup.
.LP
.PN XSetAccessControl
can generate
.PN BadAccess
and
.PN BadValue 
errors.
.LP
.sp
To enable access control, use
.PN XEnableAccessControl .
.IN "XEnableAccessControl" "" "@DEF@"
.sM
.FD 0
XEnableAccessControl\^(\^\fIdisplay\fP\^)
.br
      Display *\fIdisplay\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.LP
.eM
The
.PN XEnableAccessControl
function enables the use of the access control list at each connection setup.
.LP
.PN XEnableAccessControl
can generate a
.PN BadAccess 
error.
.LP
.sp
To disable access control, use
.PN XDisableAccessControl .
.IN "XDisableAccessControl" "" "@DEF@"
.sM
.FD 0
XDisableAccessControl\^(\^\fIdisplay\fP\^)
.br
      Display *\fIdisplay\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.LP
.eM
The
.PN XDisableAccessControl
function disables the use of the access control list at each connection setup.
.LP
.PN XDisableAccessControl
can generate a
.PN BadAccess 
error.
.bp